[RFC v2 0/3] nvme: add passthrough error logging opt-in

[Alan Adamson]

v2:
- Included Pankaj Raghav's patch 'nvme: ignore starting sector while error logging for passthrough requests'
  with a couple changes.
- Moved error_logging flag to nvme_ctrl structure
- The entire nvme-debugfs.c does not need to be guarded by #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS.
- Use IS_ENABLED((CONFIG_NVME_ERROR_LOGGING_DEBUG_FS)) to determine if error logging should be
  initialized.
- Various other nits.

  
Commit d7ac8dca938c ("nvme: quiet user passthrough command errors") disabled error
logging for user passthrough commands.  This commit adds the ability to opt in
to passthrough error logging via debugfs.

Currently nvme uses debugfs for nvme fault injection. A change is needed to extend
the nvme debugfs implementation to go beyond error injection.

Move Fault Injection to nvme-debugfs.c.  Add new config parameter (CONFIG_NVME_FAULT_INJECTION_DEBUG_FS)
which enables the compilation of Fault Injection functionality.  Other consumers 
of nvme-debugfs can be added without requiring Fault Injection.

Add new consumer of nvme-debugfs (CONFIG_NVME_ERROR_LOGGING_DEBUG_FS) that provides the
ability of passthrough error logging.

To enable passthrough error logging:
	echo 1 > /sys/kernel/debug/nvme0/error-logging

To disable passthrough error logging:
	echo 0 > /sys/kernel/debug/nvme0/error-logging

By default, passthrough error logging will remain disabled.

Signed-off-by: Alan Adamson <alan.adamson at oracle.com>